Lignin peroxidases play an important role in the biodegradation of many environmentally persistent organopollutants by the white rot fungus Phanerochaete chrysosporium. The comparison of lignin peroxidases with other peroxidases has revealed several characteristics that help to explain the unique role of these enzymes in biodegradative processes. For example, due in part to their relatively high oxidation-reduction potentials, lignin peroxidases are able to catalyze the initial oxidation of several environmental pollutants that are not oxidized by most other peroxidases. Of increasing interest is the role co-oxidants (Active oxygen species, Mn+++ complexes and veratryl alcohol radical) may play in these oxidations. The manner in which lignin peroxidases are protected from inactivation in the presence of such reactive species and, especially, reactive intermediates generated from their reducing co-substrates is also of interest. Structural features which are responsible for such properties is another important area of research interest. Thus the specific aims of the proposed research are: 1) To determine how veratryl alcohol radical, active oxygen species and other reactive species function as co-oxidants in organopollutant oxidations catalyzed by lignin peroxidases, 2) To determine the relative ability of lignin peroxidases, lactoperoxidase and PGH synthase to oxidize polycyclic aromatic hydrocarbons and selected nitrogen containing compounds, 3) To determine the relative ability of lignin peroxidases, lactoperoxidase and PGH synthase to oxidize selected environmentally persistent chlorinated organic compounds, 4) To determine the mechanism by which lignin peroxidases are protected from inactivation by reducing co-substrates that are known suicide substrates for other peroxidases, 5) To elucidate the role of calcium in lignin peroxidase structure and function.